Index: sys/kern/kern_mutex.c
===================================================================
--- sys/kern/kern_mutex.c	(revision 256019)
+++ sys/kern/kern_mutex.c	(working copy)
@@ -146,6 +146,28 @@ struct lock_class lock_class_mtx_spin = {
 struct mtx blocked_lock;
 struct mtx Giant;
 
+#define    PTR24_LSB       5                       /* lower bits all zero */
+
+#ifdef ADAPTIVE_MUTEXES
+static __inline void
+mtx_adapt_spin(struct mtx *m, volatile struct thread *owner)
+{
+	u_long rnd;
+	uint32_t backoff, tback;
+
+
+	for (backoff = LOCK_BACKOFF_INIT; mtx_owner(m) == owner &&
+	    TD_IS_RUNNING(owner); backoff <<= LOCK_BACKOFF_SHIFT) {
+		if (backoff > LOCK_BACKOFF_CAP)
+			backoff = LOCK_BACKOFF_CAP;
+		rnd = (((long)curthread >> PTR24_LSB) ^ (long)ticks);
+		tback = (uint32_t)(rnd % (backoff)) + 1;
+		for (tback = 0; tback != backoff; tback++)
+			cpu_spinwait();
+	}
+}
+#endif
+
 void
 assert_mtx(const struct lock_object *lock, int what)
 {
@@ -436,13 +458,10 @@ __mtx_lock_sleep(volatile uintptr_t *c, uintptr_t
 					CTR3(KTR_LOCK,
 					    "%s: spinning on %p held by %p",
 					    __func__, m, owner);
-				while (mtx_owner(m) == owner &&
-				    TD_IS_RUNNING(owner)) {
-					cpu_spinwait();
+				mtx_adapt_spin(m, owner);
 #ifdef KDTRACE_HOOKS
 					spin_cnt++;
 #endif
-				}
 				continue;
 			}
 		}
@@ -571,6 +590,7 @@ _mtx_lock_spin_cookie(volatile uintptr_t *c, uintp
 	int contested = 0;
 	uint64_t waittime = 0;
 #endif
+	uint32_t backoff, tback;
 
 	if (SCHEDULER_STOPPED())
 		return;
@@ -588,9 +608,14 @@ _mtx_lock_spin_cookie(volatile uintptr_t *c, uintp
 
 		/* Give interrupts a chance while we spin. */
 		spinlock_exit();
+		backoff = LOCK_BACKOFF_INIT;
 		while (m->mtx_lock != MTX_UNOWNED) {
 			if (i++ < 10000000) {
-				cpu_spinwait();
+				if (backoff > LOCK_BACKOFF_CAP)
+					backoff = LOCK_BACKOFF_CAP;
+				for (tback = 0; tback != backoff; tback++)
+					cpu_spinwait();
+				backoff <<= LOCK_BACKOFF_SHIFT;
 				continue;
 			}
 			if (i < 60000000 || kdb_active || panicstr != NULL)
@@ -624,6 +649,7 @@ thread_lock_flags_(struct thread *td, int opts, co
 #ifdef KDTRACE_HOOKS
 	uint64_t spin_cnt = 0;
 #endif
+	uint32_t backoff, tback;
 
 	i = 0;
 	tid = (uintptr_t)curthread;
@@ -661,9 +687,15 @@ retry:
 			    &contested, &waittime);
 			/* Give interrupts a chance while we spin. */
 			spinlock_exit();
+			backoff = LOCK_BACKOFF_INIT;
 			while (m->mtx_lock != MTX_UNOWNED) {
-				if (i++ < 10000000)
-					cpu_spinwait();
+				if (i++ < 10000000) {
+					if (backoff > LOCK_BACKOFF_CAP)
+						backoff = LOCK_BACKOFF_CAP;
+					for (tback = 0; tback != backoff; tback++)
+						cpu_spinwait();
+					backoff <<= LOCK_BACKOFF_SHIFT;
+				}
 				else if (i < 60000000 ||
 				    kdb_active || panicstr != NULL)
 					DELAY(1);
Index: sys/sys/lock.h
===================================================================
--- sys/sys/lock.h	(revision 256019)
+++ sys/sys/lock.h	(working copy)
@@ -189,6 +189,10 @@ struct lock_class {
 #define MPASS4(ex, what, file, line)					\
 	KASSERT((ex), ("Assertion %s failed at %s:%d", what, file, line))
 
+#define	LOCK_BACKOFF_CAP	0x400
+#define	LOCK_BACKOFF_INIT	0x01
+#define	LOCK_BACKOFF_SHIFT	0x01
+
 extern struct lock_class lock_class_mtx_sleep;
 extern struct lock_class lock_class_mtx_spin;
 extern struct lock_class lock_class_sx;